The present invention is directed to a protective plate for a bicycle chain and, more particularly, to a protective plate that is mounted near the front derailleur of the bicycle to prevent the chain from falling from the large sprocket and which is capable of securely positioning the front derailleur on the frame.
Some bicycles are equipped with three front chainrings connected to the front pedals and a plurality of rear sprockets attached to the rear wheel of the bicycle. A chain is connected between a selected front chainring and a selected rear sprocket to provide driving force from the pedals to the rear wheel. A front derailleur is used to position the chain on the selected front chainring, and a rear derailleur is used to position the chain on the selected rear sprocket. The various combinations of front and rear sprockets provide a wide range of gear ratios to accommodate a wide range of riding conditions.
If the front derailleur is not adjusted properly, there is a risk that the chain will fall from the smallest chainring when the chain is being shifted from the middle chainring to the smallest chainring. As a result, the chain often jams between the smallest sprocket and the bicycle frame, thus requiring the rider to dismount the bicycle and reattach the chain to the sprocket. Since the chain often jams between the smallest sprocket and the bicycle frame with much force, unjamming the chain can be very difficult. Thus, it is desirable to prevent such jamming if possible.
Finally, adjusting the front derailleur includes properly setting the vertical position of the front derailleur on the seat tube. This can prove very difficult and time consuming, since very close tolerances are usually required for proper operation.
One apparatus used with a front derailleur for preventing chain derailing while facilitating the positioning of the front derailleur on the bicycle is disclosed in U.S. patent application Ser. No. 09/023,821 entitled "Protective Plate for a Bicycle Chain" filed Feb. 13, 1998. That patent application discloses a protective plate for attachment to a bicycle frame, wherein the protective plate includes a support body having a first side for facing laterally toward the bicycle frame, a second side for facing laterally away from the bicycle frame, a lower portion, and an upper portion. The lower portion of the first side of the support body is structured to align with a bottom bracket of the bicycle, and a positioning abutment member is disposed on the upper portion of the first side of the support body. An upper surface of the positioning abutment member forms a positioning abutment for positioning a front derailleur to the bicycle frame. Additionally, a chain guiding abutment may be formed on the upper portion of the second side of the support body for guiding the chain as the chain shifts from a larger chainring to a smaller chainring. In this apparatus, the upper portion of the support body is not securely fixed to the bicycle frame, so some flexure of the support body can occur during very rough riding, thus decreasing the effectiveness of the front derailleur.
The assignee of the present invention also has sold a model FD-M950 front derailleur with a support plate that mounts directly to the bottom bracket. That derailleur is prior art to this invention. To save weight, this support plate is formed relatively thin. However, such a thin plate may flex and alter the optimal positioning of the derailleur. On the other hand, it is undesirable to make the plate thicker because that would undesirably increase the weight of the plate.